It is the common practice to produce a diarylamine by the Ullmann condensation reaction of an aromatic halide and an arylamine derivative (Chem. Ber., 36, 2382(1902)), Chem. Ber., 40, 4541(1907)) or by subjecting an arylamine to self condensation or subjecting an arylamine and the corresponding arylamine hydrochloride to condensation reaction.
The production by the Ullman reaction is accompanied with the problems that the raw material aromatic halide is expensive and a step for hydrolyzing an amide formed by the condensation reaction is necessary.
In the condensation reaction of an arylamine, on the other hand, it was reported that a diphenylamine was available by heating of aniline and aniline hydrochloride to 300.degree. C. in a solventless manner under a high pressure (Zeitschr. Chem., 438(1866)) and since then, addition of various effective catalysts have been proposed. For example, disclosed are a process of adding anhydrous ferrous chloride (U.S. Pat. No. 2,447,044), a process of adding ammonium chloride (U.S. Pat. No. 2,820,829), a process of adding anhydrous aluminum chloride and ammonium chloride (U.S. Pat. No. 2,645,662), a process of adding anhydrous ferrous chloride and ammonium bromide, and a process of adding cobalt chloride, stannous chloride, cupric chloride, zinc chloride, manganese chloride or the like, and ammonium chloride (U.S. Pat. No. 2,120,966).
In any one of the above-described processes, however, the reaction is conducted under severe conditions of 300 to 400.degree. C. and a high pressure, which requires special equipment such as pressure reactor.
As processes comprising the reaction under a normal pressure, proposed are a process (Zh. Prikl. Khim. (Leningrag). Vol.9, 502(1936)) for synthesizing a diphenylamine by reacting aniline and aniline hydrochloride in the presence of aluminum chloride as a catalyst at 220 to 240.degree. C. for 20 to 25 hours and a process for preparing di-p-tolylamine which comprises reacting p-toluidine in an aromatic solvent in the presence of anhydrous aluminum chloride and ammonium chloride (Unexamined published Japanese patent application No. Hei. 6-100504). These processes, however, need at least 15 hours to complete the reaction and in addition, the diarylamine obtained by each of these processes is not so highly pure as to be usable as an intermediate for the raw material of an electronic material.